Network structures and dynamics of dry and swollen poly(acrylate)s. Characterization of high- and low-frequency motions as revealed by suppressed or recovered intensities (SRI) analysis of 13C NMR

We recorded temperature-dependent high-resolution 13C NMR spectra of dry and swollen poly(acrylate)s [poly(2-methoxyethyl acrylate) (PMEA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(tetrahydrofurfuryl acrylate) (PTHFA)] by dipolar decoupled-magic angle spinning (DD-MAS) and cross-polarization-magic angle spinning (CP-MAS) methods, to gain insight into their network structures and dynamics. Suppressed or recovered intensities (SRI) analysis of 13C CP-MAS and DD-MAS NMR was successfully utilized, to reveal portions of dry and swollen polymers which undergo fast and slow motions with fluctuation frequencies in the order of 108 Hz and 104–105 Hz, respectively. Fast isotropic motions with frequency higher than 108 Hz at ambient temperature were located to the portions in which 13C CP-MAS NMR signals of swollen PMEA were selectively suppressed. In contrast, low-frequency motion was identified to the portions in which 13C DD-MAS (and CP-MAS) signals are most suppressed at the characteristic suppression temperature(s) Ts. Network of PMEA gels (containing 7 wt% of water) turns out to be formed by partial association of backbones only, as manifested from their Ts gradient at lowered temperature, whereas networks of PHEMA (containing 40 wt% of water) and PTHFA (9 wt% of water) gels are tightly formed through mutual inter-chain associations of both backbones and side-chains, as viewed from the raised Ts values for both near at ambient temperature. It is also interesting to note that flexibility of gel network (PMEA > PTHFA > PHEMA) characterized by the suppression temperature Ts (PMEA < PTHFA < PHEMA) is well related with a characteristic parameter for biocompatibility such as the production of TAT (thrombin–antithrombin III complex) as a marker of activation of the coagulation system.